1. Field of Invention
The present invention relates to the technology of a light-emitting diode (LED), and more particularly to an electronic candle and an electronic night lamp.
2. Related Art
After the industry revolution, the human beings use a lot of fossil fuel, deforest, use the carbide containing chlorine and fluorine and participate in the enlivened agrarian and industrial activities. Thus, the gases (i.e., the greenhouse gases GHG), such as carbon dioxide, methane, nitrous oxide, fluorine chlorine carbide, sulphur hexafluoride (SF6), perfluorocarbons (PFCs) and hydrogen fluorine carbide (HFCs), capable of absorbing the longwave radiation are greatly increased to cause the global warming phenomenon and thus the global greenhouse effect phenomenon. Because the global warming may dangerously cause the extremely abnormal influence of the global climate, and thus the significant impact on the deterioration of the ecology environment, the reduction of energy consumption is greatly pushed in various countries.
FIG. 1 shows a conventional electronic night lamp. Referring to FIG. 1, the electronic night lamp includes a light emitting element 101, a casing 102 and a light source detector 103. The light source detector 103 is mainly utilized to detect the environmental brightness, and the electronic night lamp may judge whether the light emitting element 101 is lighted up according to the detected environmental brightness.
A light dependent resistor is widely used in the light source detector 103. The main chemical substance of the light dependent resistor is cadmium sulfide (CdS) or cadmium selenide (CdSe). After the light dependent resistor is illuminated by light, its resistance value is decreased. The change of the resistance value of the light dependent resistor illuminated by the light becomes larger as the area of the CdS or CdSe deposition film of the light dependent resistor becomes larger. So, the deposition film usually has the zigzag shape to enlarge its area. FIG. 2 is a schematic illustration showing a structure of a conventional light dependent resistor.
However, the price of the light dependent resistor is very high. In addition, the European Union has published Restriction of Hazardous Substances (RoHS), which prohibits the import of the electronic apparatus containing lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl or polybrominated diphenyl ethers (PBDEs). In response to the new rule of the European Union, Bureau of Standards, Metrology & Inspection in Taiwan also has specified the “Particular Criteria Governing Designated Testing Laboratories For Hazardous Substances”. Thus, the light dependent resistor containing the cadmium sulfide (CdS) or the cadmium selenide (CdSe) cannot satisfy the specifications of various countries. In addition, although the manufacturer for manufacturing the light dependent resistor has disclosed the cadmium-free light dependent resistor, its price is relatively high.